1. Augmentation of specific antitumor immune T cells isolated from tumor site: T cells isolated from FBL-3 ascites growth were found to be highly cytotoxic in vitro but lacked long lasting in vivo antitumor effect. When these T cells were selectively grown in vitro with IL2, not only their in vitro cytotoxic activity was further augmented; they were found to give long lasting protection in the in vivo tumor neutralization test. 2. Regulation of T cell-mediated immunity by macrophages and prostaglandins: in the normal immune response, macrophages and prostaglandins appear to play a central role in the regulation of CTL (cytotoxic T lymphocytes) activation. When the restriction by prostaglandin was removed, a lymphokine is produced through the interaction of macrophages and lymphocytes. This lymphokine appeared to be distinct from IL1 or IL2 and was essential for providing the differentiation signal for the differentiation of CTL precursors into CTL. These lymphokines may also be involved in the networks and circuits which regulate the immune surveillance of tumor growth.